Sales tax on SaaS is one of the fastest-growing compliance headaches for startups.
Sales tax compliance for SaaS is the process of determining where you have a tax collection obligation (nexus), registering in those jurisdictions, collecting the correct rate at checkout, and remitting on the required schedule. It is deeply unglamorous, easy to defer, and one of the most common negative surprises in acquisition due diligence. Getting it under control at Series A saves five-figure or six-figure back-tax exposure at Series C.
You have sales tax nexus in a US state when you meet either (a) physical nexus — employee, office, or inventory in the state, or (b) economic nexus — post-Wayfair thresholds, commonly $100K in sales or 200 transactions per year into the state (varies: CA is $500K, TX is $500K, NY is $500K + 100 transactions). Track sales by state monthly; the moment you cross a threshold, you have a legal obligation to register and collect. Not all states tax SaaS — as of 2026, roughly 20 US states tax SaaS at the state level; some cities tax on top; the map keeps changing. Do not rely on tribal knowledge; use a tool that tracks the ruleset.
Once you cross nexus in a state, register with the state Department of Revenue (each state has its own portal), receive a sales tax permit, begin collecting at the required rate, and file returns on the state's schedule (monthly for high volume, quarterly for medium, annually for low). Registration is not retroactive — filing when you crossed nexus 8 months ago exposes back taxes plus penalties plus interest. Better to register and voluntarily disclose than to be discovered. Deregister when you drop below thresholds (some states require it; some don't) to reduce filing burden.
EU VAT on B2C digital services: register in one EU country via VAT OSS (One Stop Shop) and remit VAT to that country, which distributes to member states. Applies from the first euro of B2C sales. B2B EU sales use reverse charge (customer self-assesses VAT); collect and validate VAT numbers. UK, Canada (GST/HST/QST), Australia (GST), New Zealand (GST), and a growing list of countries (India GST, Singapore GST, Saudi Arabia VAT, UAE VAT) have registration thresholds and their own rules. Digital services taxes (DSTs) in France, UK, Italy add another layer for large sellers.
Manual sales tax at any meaningful scale is a losing game. Purpose-built tools: Anrok (SaaS-focused, US + international), Stripe Tax (bundled if you use Stripe), Avalara (enterprise standard, powerful and expensive), TaxJar (SMB-friendly), Sphere (SaaS + international). Integration: connect to your billing system, tool determines nexus continuously, calculates correct rate at checkout, files returns on your behalf. Cost: $500-3,000/month at Series A scale, dropping to a fraction of a percent of billing at scale. Payback is fast — one missed jurisdiction discovered in diligence costs more than years of software fees.
If you already have unregistered nexus, do not just start collecting forward — that leaves a historical liability visible in any audit or diligence. Options: (1) Voluntary Disclosure Agreement (VDA) — negotiate with the state to limit lookback (usually 3-4 years) and waive penalties in exchange for coming forward and paying back taxes. Most cost-effective for material exposure. (2) Streamlined Sales Tax registration for participating states. (3) Simply file back returns for the exposed period. Work with a sales tax accountant (Anrok, Miles Consulting, Peisner Johnson) — this is one of the few areas where DIY costs more than the fees.
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